Postobstructive urinary tract dysfunction is a disorder with extremely high morbidity and devastating social and psychological consequence, resulting in a complex of symptoms including incontinence, increased frequency of urination, and an inappropriate sense of urinary urgency, all of which appear to result from abnormal contractile activity of the smooth muscle lining the bladder. In this proposal we seek to understand the generation of rhythmic or phasic contractile activity in the normal and postobstructed urinary bladder in vivo. Although the study of the cellular signals underlying phasic activity is extraordinarily difficult in vivo, it is important to understand this activity in the context of neural and hormonal inputs that play an important role in the regulation of contractile activity. We have recently developed methods to monitor intracellular free Ca2+ in vivo through the development of transgenic mice expressing a novel high signal-noise, genetically encoded Ca2+ indicator. GCaMP2, the Ca2+ indicator, is stable at physiological temperatures and approaches the brightness of GFP, enabling sustained, high resolution recording of cellular Ca2+ transients in the living mouse. Mice in which this molecule is highly expressed in urinary bladder smooth muscle have been created and will be used to visualize cellular Ca2+ signals in vivo. We will use these mice to more fully understand the dysfunction associated with urinary tract outlet obstruction. The basis of abnormal contractile activity in postobstructive mice that develop spontaneous bladder overactivity will be studied to understand the cellular and molecular basis for abnormal bladder contractions. We hypothesize that bladder hyperactivity occurs secondary to the development of abnormal pacemaker activity and anomalous Ca2+ waves associated with dysregulated Ca2+ release from the sarcoplasmic reticulum (SR) of smooth muscle or Interstitial Cells of Cajal (ICC). To test this hypothesis, we will image phasic Ca2+ signals in smooth muscle cells under normal conditions, seek to understand the cellular and molecular basis for spontaneous activity, determine the extent to which this pattern is disturbed by sustained outflow obstruction, and test whether abnormal activity arises due to alterations in SR Ca2+ release in muscle or changes in the activity of pacemaker cells in the urinary bladder. These findings should provide a clearer understanding of smooth muscle dysfunction associated with urinary tract outflow obstruction.